Process for making extruded receiver and carrier layer for receiving element for use in thermal dye transfer

ABSTRACT

A process for making a thermal dye transfer receiver element comprising: 
     a) coextruding a dye image-receiving layer with an orientable thermoplastic resin to form a cast film; 
     b) stretching the cast film to reduce the thickness of the dye image-receiving layer and to produce an oriented composite film; and 
     c) laminating the oriented composite film to a support.

This invention relates to a process for making dye-receiving elementsused in thermal dye transfer, and more particularly to receivingelements made by coextruding a dye image-receiving layer and anorientable thermoplastic resin carrier layer prior to stretching andlaminating to a support.

In recent years, thermal transfer systems have been developed to obtainprints from pictures which have been generated electronically from acolor video camera. According to one way of obtaining such prints, anelectronic picture is first subjected to color separation by colorfilters. The respective color-separated images are then converted intoelectrical signals. These signals are then operated on to produce cyan,magenta and yellow electrical signals. These signals are thentransmitted to a thermal printer. To obtain the print, a cyan, magentaor yellow dye-donor element is placed face-to-face with a dye-receivingelement. The two are then inserted between a thermal printing head and aplaten roller. A line-type thermal printing head is used to apply heatfrom the back of the dye-donor sheet. The thermal printing head has manyheating elements and is heated up sequentially in response to the cyan,magenta and yellow signals. The process is then repeated for the othertwo colors. A color hard copy is thus obtained which corresponds to theoriginal picture viewed on a screen. Further details of this process andan apparatus for carrying it out are contained in U.S. Pat. No.4,621,271, the disclosure of which is hereby incorporated by reference.

U.S. Pat. No. 4,695,286 discloses dye-receiving elements used in thermaldye transfer which comprise a polymeric dye image-receiving layer coatedon a base or support. These dye image-receiving layers have typicallybeen applied to a receiver support by a solvent coating process. Thereis a problem with solvent coating processes, however, in that they arerather expensive and create environmentally unfriendly waste productssuch as solvent based solutions as well as solvent vapor.

U.S. Ser. No. 801,223 of Daly, filed Dec. 3, 1991, discloses extrudablereceiver layers. While these receiver polymers eliminate the solventcoating disadvantages, there is a problem with these materials in thatit is difficult to apply them in thin layers onto receiver supports.Receiver layer thicknesses produced by the solvent coating process areon the order of 1-10 μm. Typically the minimum layer thickness for anextruded film is 25 μm. Receiver layer polymers are rather expensive toproduce and need not be present at a thickness of more than 10 μm.

U.S. Pat. No. 4,912,085 discloses that receiver layers can be coextrudedwith thermoplastic receiver supports and then stretched. However, thistechnique is limited since it can only be applied to supports which canbe stretched. It is an object of this invention to provide a techniquewhich could be applied to non-stretchable supports such as paper.

U.S. Pat. No. 5,244,861, dye-receiving elements are disclosed wherein adye image-receiving layer is coated onto a composite film laminated to asupport. The composite film comprises a microvoided thermoplastic corelayer and at least one substantially void-free thermoplastic surfacelayer. There is a problem with this technique in that the dyeimage-receiving layer is solvent coated onto the support with thedisadvantages noted above.

It is an object of the invention to provide a process for preparingreceiving elements with both the ecological and cost advantages of filmextrusion. It is another object of the invention to provide a processfor preparing receiving elements with thin dye receiving layers. It isstill another object of this invention to provide a process forpreparing receiving elements which are formed on stretchable as well asnon-stretchable supports such as paper.

These and other objects are achieved in accordance with this invention,which comprises a process for making a thermal dye transfer receiverelement comprising:

a) coextruding a dye image-receiving layer with an orientablethermoplastic resin to form a cast film;

b) stretching the cast film to reduce the thickness of the dyeimage-receiving layer and to produce an oriented composite film; and

c) laminating the oriented composite film to a support.

The cast film is formed by coextruding an orientable thermoplastic resinsuch as a semicrystalline polymer, which may optionally be filled withvoid-initiating organic or inorganic particles, with a dyeimage-receiving material onto a chilled casting drum. The quenchedcomposite film is then biaxially oriented by stretching in mutuallyperpendicular directions at a temperature above the glass transitiontemperature (Tg) of the polymers. If void-initiating particles arepresent, then voids are created around each of the particles in thecore. The film may be stretched in one direction and then in a seconddirection or may be simultaneously stretched in both directions.

After the cast film has been stretched, it is heat set to a temperaturesufficient to crystallize the polymer while restraining to some degreethe film against retraction in both directions of stretching.Non-microvoided films can be formed in a similar fashion by excludingthe void-initiating particles from the core. While films withoutmicrovoids do not offer the same level of image uniformity improvementin thermal dye transfer receiver structures, they can provide asignificant improvement.

In this invention, the receiving layer polymer is stretched, thusthinning the expensive receiver polymer skin and, in the case of thecarrier or core layer containing void-initiating particles, producingmicrovoids. This new composite film can then be laminated to eitherstretchable or non-stretchable receiver supports to complete a receiverelement which does not require the expensive and environmentally unsoundsolvent coating step.

Composite films with thermal dye transfer receiver skins have astructure as shown below:

    ______________________________________                                        Dye Receiver Layer Skin                                                       Optional Adhesive Tie Layer                                                   Thermoplastic Core (with or without microvoids)                               Optional Thermoplastic Layer                                                  Optional Skin Layer                                                           ______________________________________                                    

It is possible to produce a simple two-layer composite structure withjust a receiver layer skin and a thermoplastic core. However, it isdifficult to prepare receiver polymers with sufficient adhesion to thethermoplastic core to remain attached to the core after the stretchingprocess. To solve this problem, an adhesive tie layer can be coextrudedbetween the receiver layer and the thermoplastic core. This tie polymermust have excellent adhesion to both the receiver polymer and thethermoplastic core to function well.

Examples of tie layers useful in the invention include polyester tielayers such as Admer AT 507® (Mitsui Petrochemicals America, Ltd.).These materials have been found to provide excellent adhesion betweenpolyester dye receiver skins and polyolefin thermoplastic cores. It isoften desirable to maintain symmetry in these coextruded composite filmstructures for a stable manufacturing process, therefore an optionalthermoplastic layer and skin layer may be required on the backside ofthe core.

Other examples of tie layers useful in the invention include polyesters,polycarbonates, acrylic copolymers, polyolefins and oxidizedpolyolefins, polymethanes and polyamides. They may be employed at acoverage of at least about 0.1 g/m².

The core of the composite film should be from 15 to 95% of the totalthickness of the film, preferably from 30 to 85% of the total thickness.The receiving layer should thus be from 5 to 85% of the film, preferablyfrom 15 to 70% of the thickness. The density (specific gravity) of thecomposite film should be between 0.2 and 1.0 g/cm³, preferably between0.3 and 0.7 g/cm³. As the core thickness becomes less than 30% or as thespecific gravity is increased above 0.7 g/cm³, the composite film startsto lose useful compressibility and thermal insulating properties. As thecore thickness is increased above 85% or as the specific gravity becomesless than 0.3 g/cm³, the composite film becomes less manufacturable dueto a drop in tensile strength and it becomes more susceptible tophysical damage. The total thickness of the composite film can rangefrom 20 to 150 μm, preferably from 30 to 70 μm. Below 30 μm, themicrovoided films may not be thick enough to minimize any inherentnon-planarity in the support and would be more difficult to manufacture.At thicknesses higher than 70 μm, little improvement in either printuniformity or thermal efficiency are seen, and so there is littlejustification for the further increase in cost for extra materials.

"Void" is used herein to mean devoid of added solid and liquid matter,although it is likely the "voids" contain gas. The void-initiatingparticles which remain in the finished packaging film core should befrom 0.1 to 10 μm in diameter, preferably round in shape, to producevoids of the desired shape and size. The size of the void is alsodependent on the degree of orientation in the machine and transversedirections. Ideally, the void would assume a shape which is defined bytwo opposed and edge contacting concave disks. In other words, the voidstend to have a lens-like or biconvex shape. The voids are oriented sothat the two major dimensions are aligned with the machine andtransverse directions of the film. The Z-direction axis is a minordimension and is roughly the size of the cross diameter of the voidingparticle. The voids generally tend to be closed cells, and thus there isvirtually no path open from one side of the voided-core to the otherside through which gas or liquid can traverse.

The void-initiating material may be selected from a variety ofmaterials, and should be present in an amount of about 5-50% by weightbased on the weight of the core matrix polymer. Preferably, thevoid-initiating material comprises a polymeric material. When apolymeric material is used, it may be a polymer that can be melt-mixedwith the polymer from which the core matrix is made and be able to formdispersed spherical particles as the solution is cooled down. Examplesof this would include nylon dispersed in polypropylene, polybutyleneterephthalate in polypropylene, or polypropylene dispersed inpolyethylene terephthalate. If the polymer is preshaped and blended intothe matrix polymer, the important characteristic is the size and shapeof the particles. Spheres are preferred and they can be hollow or solid.These spheres may be made from cross-linked polymers which are membersselected from the group consisting of an alkenylaromatic compound havingthe general formula Ar×C(R)=CH₂, wherein Ar represents an aromatichydrocarbon radical, or an aromatic halohydrocarbon radical of thebenzene series and R is hydrogen or the methyl radical; acrylate-typemonomers include monomers of the formula CH₂ =C(R')×C(O)(OR) wherein Ris selected from the group consisting of hydrogen and an alkyl radicalcontaining from about 1 to 12 carbon atoms and R' is selected from thegroup consisting of hydrogen and methyl; copolymers of vinyl chlorideand vinylidene chloride, acrylonitrile and vinyl chloride, vinylbromide, vinyl esters having formula CH₂ =CH(O)COR, wherein R is analkyl radical containing from 2 to 18 carbon atoms; acrylic acid,methacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaricacid, oleic acid, vinylbenzoic acid; the synthetic polyester resinswhich are prepared by reacting terephthalic acid and dialkylterephthalics or ester-forming derivatives thereof, with a glycol of theseries HO(CH₂)_(n) OH wherein n is a whole number within the range of2-10 and having reactive olefinic linkages within the polymer molecule,the above described polyesters which include copolymerized therein up to20 percent by weight of a second acid or ester thereof having reactiveolefinic unsaturation and mixtures thereof, and a cross-linking agentselected from the group consisting of divinylbenzene, diethylene glycoldimethacrylate, diallyl fumarate, diallyl phthalate and mixturesthereof.

Examples of typical monomers for making the above crosslinked polymerinclude styrene, butyl acrylate, acrylamide, acrylonitrile, methylmethacrylate, ethylene glycol dimethacrylate, vinylpyridine, vinylacetate, methyl acrylate, vinylbenzyl chloride, vinylidene chloride,acrylic acid, divinylbenzene, acrylamidomethylpropanesulfonic acid,vinyltoluene, etc. Preferably, the cross-linked polymer is polystyreneor poly(methyl methacrylate). Most preferably, it is polystyrene and thecross-linking agent is divinylbenzene.

Processes well known in the art yield non-uniformly sized particles,characterized by broad particle size distributions. The resulting beadscan be classified by screening the product beads spanning the range ofthe original distribution of sizes. Other processes such as suspensionpolymerization, limited coalescence, directly yield very uniformly sizedparticles.

The void-initiating materials may be coated with a slip agent tofacilitate voiding. Suitable slip agents or lubricants .includecolloidal silica, colloidal alumina, and metal oxides such as tin oxideand aluminum oxide. The preferred slip agents are colloidal silica andalumina, most preferably, silica. The cross-linked polymer having acoating of slip agent may be prepared by procedures well known in theart. For example, conventional suspension polymerization processeswherein the slip agent is added to the suspension are preferred. As theslip agent, colloidal silica is preferred.

The void-initiating particles can also be inorganic spheres, includingsolid or hollow glass spheres, metal or ceramic beads or inorganicparticles such as clay, talc, barium sulfate, calcium carbonate. Theimportant thing is that the material does not chemically react with thecore matrix polymer to cause one or more of the following problems: (a)alteration of the crystallization kinetics of the matrix polymer, makingit difficult to orient, (b) destruction of the core matrix polymer, (c)destruction of the void-initiating particles, (d) adhesion of thevoid-initiating particles to the matrix polymer, or (e) generation ofundesirable reaction products, such as toxic or high color moieties.

Suitable classes of thermoplastic polymers for the core matrix-polymerof the composite film include polyolefins, polyesters, polyamides,polycarbonates, cellulosic esters, polystyrene, polyvinyl resins,polysulfonamides, polyethers, polyimides, poly(vinylidene fluoride),polyurethanes, poly(phenylene sulfides), polytetrafluoroethylene,polyacetals, polysulfonates, polyester ionomers, and polyolefinionomers. Copolymers and/or mixtures of these polymers can be used.

Suitable polyolefins for the core matrix-polymer of the composite filminclude polypropylene, polyethylene, polymethylpentene, and mixturesthereof. Polyolefin copolymers, including copolymers of ethylene andpropylene are also useful.

Suitable polyesters for the core matrix-polymer of the composite filminclude those produced from aromatic, aliphatic or cycloaliphaticdicarboxylic acids of 4-20 carbon atoms and aliphatic or alicyclicglycols having from 2-24 carbon atoms. Examples of suitable dicarboxylicacids include terephthalic, isophthalic, phthalic acids,naphthalenedicarboxylic acid, succinic, glutaric, adipic, azelaic,sebacic, fumaric, maleic, itaconic, 1,4-cyclohexanedicarboxylic,sodiosulfoisophthalic acids and mixtures thereof. Examples of suitableglycols include ethylene glycol, propylene glycol, butanediol,pentanediol, hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol,other polyethylene glycols and mixtures thereof. Such polyesters arewell known in the art and may be produced by well known techniques,e.g., those described in U.S. Pat. Nos. 2,465,319 and 2,901,466.Preferred continuous matrix polyesters are those having repeat unitsfrom terephthalic acid or naphthalenedicarboxylic acid and at least oneglycol selected from ethylene glycol, 1,4-butanediol and1,4-cyclohexanedimethanol. Poly(ethylene terephthalate), which may bemodified by small amounts of other monomers, is especially preferred.Other suitable polyesters include liquid crystal copolyesters formed bythe inclusion of suitable amount of a co-acid component such asstilbene-dicarboxylic acid. Examples of such liquid crystal copolyestersare those disclosed in U.S. Pat. Nos. 4,420,607, 4,459,402 and4,468,510.

Useful polyamides for the core matrix-polymer of the composite filminclude Nylon 6, Nylon 66, and mixtures thereof. Copolymers ofpolyamides are also suitable continuous phase polymers. An example of auseful polycarbonate is bisphenol-A polycarbonate. Cellulosic esterssuitable for use as the continuous phase polymer of the composite filmsinclude cellulose nitrate, cellulose triacetate, cellulose diacetate,cellulose acetate propionate, cellulose acetate butyrate, and mixturesor copolymers thereof. Useful polyvinyl resins include poly(vinylchloride), poly(vinyl acetal), and mixtures thereof. Copolymers of vinylresins can also be utilized.

In a preferred embodiment of the invention, the thermoplastic materialsused as the core for the composite films in this invention arepropylene/ethylene copolymers manufactured by Eastman Chemicals Company.These polyolefins were compounded with 15 wt-% of 5 μm diameterpolystyrene beads crosslinked with divinylbenzene and coated withcolloidal silica. The process for preparing these materials and blendsis described in U.S. Pat. No. 5,244,861.

Addenda may be added to the core matrix to improve the whiteness ofthese films. This would include any process which is known in the artincluding adding a white pigment, such as titanium dioxide, bariumsulfate, clay, or calcium carbonate. This would also include addingfluorescing agents which absorb energy in the UV region and emit lightlargely in the blue region, or other additives which would improve thephysical properties of the film or the manufacturability of the film.

The coextrusion, quenching, orienting, and heat setting of thesecomposite films may be effected by any process which is known in the artfor producing oriented film, such as by a flat film process or a bubbleor tubular process. The flat film process involves extruding the blendthrough a slit dye and rapidly quenching the extruded web upon a chilledcasting drum so that the core matrix polymer component of the film andthe skin components(s) are quenched below their glass transitiontemperatures (Tg). The quenched film is then biaxially oriented bystretching in mutually perpendicular directions at a temperature abovethe glass transition temperature of the matrix polymers and the skinpolymers. The film may be stretched in one direction and then in asecond direction or may be simultaneously stretched in both directions.

After the film has been stretched it is heat set by heating to atemperature sufficient to crystallize the polymers while restraining tosome degree the film against retraction in both directions ofstretching.

The support to which the microvoided composite films are laminated asbase for the dye-receiving element prepared by the process of theinvention may be a polymeric, a synthetic paper, or a cellulose fiberpaper support, or laminates thereof.

Preferred cellulose fiber paper supports include those disclosed in U.S.Pat. No. 5,250,496, the disclosure of which is incorporated byreference. When using a cellulose fiber paper support, it is preferableto extrusion laminate the microvoided composite films using a polyolefinresin. During the lamination process, it is desirable to maintainminimal tension of the microvoided packaging film in order to minimizecurl in the resulting laminated receiver support. The backside of thepaper support (i.e., the side opposite to the microvoided composite filmand receiver layer) may also be extrusion coated with a polyolefin resinlayer (e.g., from about 10 to 75 g/m²), and may also include a backinglayer such as those disclosed in U.S. Pat. Nos. 5,011,814 and 5,096,875,the disclosures of which are incorporated by reference. For highhumidity applications (>50% RH), it is desirable to provide a backsideresin coverage of from about 30 to about 75 g/m², more preferably from35 to 50 g/m², to keep curl to a minimum.

In one preferred embodiment, in order to produce receiver elements witha desirable photographic look and feel, it is preferable to userelatively thick paper supports (e.g., at least 120 μm thick, preferablyfrom 120 to 250 μm thick) and relatively thin microvoided compositefilms (e.g., less than 50 μm thick, preferably from 20 to 50 μm thick,more preferably from 30 to 50 μm thick).

In another embodiment of the invention, in order to form a receiverelement which resembles plain paper, e.g. for inclusion in a printedmultiple page document, relatively thin paper or polymeric supports(e.g., less than 80 μm, preferably from 25 to 80 μm thick) may be usedin combination with relatively thin microvoided composite films (e.g.,less than 50 μm thick, preferably from 20 to 50 μm thick, morepreferably from 30 to 50 μm thick).

The dye image-receiving layer of the receiving elements prepared by theprocess of the invention may comprise, for example, a polycarbonate, apolyurethane, a polyester, poly(vinyl chloride),poly(styrene-co-acrylonitrile), poly(caprolactone) or mixtures thereof.Polyester receiver polymers as disclosed and described in Daly copendingU.S. Ser. No. 801,223 are also useful in this invention. Thesepolyesters are copolymers condensed from cyclohexanedicarboxylate and a50/50 mole-% mixture of ethylene glycol and bisphenol-A-diethanol(COPOL)®. The dye image-receiving layer may be present in any amountwhich is effective for the intended purpose. In general, good resultshave been obtained at a concentration of from about 1 to about 10 g/m².

Dye-donor elements that are used with the dye-receiving element preparedby the process of the invention conventionally comprise a support havingthereon a dye containing layer. Any dye can be used in the dye-donoremployed with the receiving elements prepared according to the inventionprovided it is transferable to the dye-receiving layer by the action ofheat. Especially good results have been obtained with sublimable dyes.Dye donors applicable for use in the present invention are described,e.g., in U.S. Pat. Nos. 4,916,112, 4,927,803 and 5,023,228, thedisclosures of which are incorporated by reference.

As noted above, dye-donor elements are used to form a dye transferimage. Such a process comprises imagewise-heating a dye-donor elementand transferring a dye image to a dye-receiving element as describedabove to form the dye transfer image.

In a preferred embodiment of the invention, a dye-donor element isemployed which comprises a poly(ethylene terephthalate) support coatedwith sequential repeating areas of cyan, magenta and yellow dye, and thedye transfer steps are sequentially performed for each color to obtain athree-color dye transfer image. Of course, when the process is onlyperformed for a single color, then a monochrome dye transfer image isobtained.

Thermal printing heads which can be used to transfer dye from dye-donorelements to the receiving elements prepared according to the inventionare available commercially. There can be employed, for example, aFujitsu Thermal Head (FTP-040 MCS001), a TDK Thermal Head F415 HH7-1089or a Rohm Thermal Head KE 2008-F3. Alternatively, other known sources ofenergy for thermal dye transfer may be used, such as lasers as describedin, for example, GB No. 2,083,726A.

A thermal dye transfer assemblage using the invention comprises (a) adye-donor element, and (b) a dye-receiving element as described above,the dye-receiving element being in a superposed relationship with thedye-donor element so that the dye layer of the donor element is incontact with the dye image-receiving layer of the receiving element.

When a three-color image is to be obtained, the above assemblage isformed on three occasions during the time when heat is applied by thethermal printing head. After the first dye is transferred, the elementsare peeled apart. A second dye-donor element (or another area of thedonor element with a different dye area) is then brought in registerwith the dye-receiving element and the process repeated. The third coloris obtained in the same manner.

The following examples are provided to further illustrate the invention.

Example 1

Composite films were prepared by coextruding the structure shown below:

    ______________________________________                                                                  Extrusion                                           Polymer                   Temp.                                               ______________________________________                                        64 μm Thick COPOL ® Dye Receiver                                                                 250° C.                                      Layer                                                                         64 μm Thick Admer ® AT 507 Adhesive Tie                                                          250° C.                                      Layer                                                                         254 μm Thick Propylene/Ethylene Copolymer                                                            307° C.                                      & Styrene/Divinylbenzene Microbeads                                           ______________________________________                                    

These films were coextruded with the temperature profile shown above andcast onto a 9° C. chilled drum and quenched. They were then stretched3.3 times in both the machine and cross directions at the temperaturesshown in Table 1. The films were then heat set at the temperatures shownin Table 1 and rolled up onto a core. The film variations which wereprepared are summarized in Table 1.

                  TABLE 1                                                         ______________________________________                                        Receiver Elements With Varying Core Layers                                    Receiver Material: COPOL ®                                                Tie layer: AT 507                                                                                  Temperature (°C.)                                 Sample # Core Layer        Stretch  Heat Set                                  ______________________________________                                        1        P5-001 (94.5% propyl-                                                                           105      111                                                ene/5.5% ethylene)                                                   2        P4-005 (100% propylene)                                                                         145      150                                       3        P6-008 (87.5% propyl-                                                                           135      140                                                ene/12.5% ethylene)                                                  4        P5-003 (99.6% propyl-                                                                           146      150                                                ene/0.4% ethylene)                                                   ______________________________________                                    

Each of these films was then extrusion-laminated onto a support withpolyethylene (12 g/m²) containing anatase titanium dioxide (13 wt. %)and a stilbene-benzoxazole optical brightner (0.03 wt. %). The supportwas a paper stock (120 μm thick, made from a 1:1 blend of Pontiac Maple51 (a bleached maple hardwood kraft of 0.5 mm length weighted averagefiber length), Consolidated Pontiac, Inc.) and Alpha Hardwood Sulfite (ableached red alder hardwood sulfite of 0.69 mm average fiber lengthWeyerhaeuser Paper Co.). The backside of the stock support was extrusioncoated with high density polyethylene (25 g/m²).

Magenta dye containing thermal dye transfer donor elements were preparedby coating on 6 μm poly(ethylene terephthalate) support:

a) a subbing layer of Tyzor TBT® (a titanium tetra-n-butoxide) (duPontCo.) (0.12 g/m²) from 1-butanol; and

b) a dye-layer containing the magenta dyes illustrated below (0.12 and0.13 g/m²) and S-363 (Shamrock Technologies, Inc.) (a micronized blendof polyolefin and oxidized polyolefin particles) (0.016 g/m²), in acellulose acetate propionate binder (2.5% acetyl, 45% propionyl) (0.40g/m²) from a toluene, methanol, and cyclopentanone solvent mixture.

On the backside of the dye donor element was coated:

a) a subbing layer of Tyzor TBT® (a titanium tetra-n-butoxide) (duPontCo.) (0.12 g/m²) from 1-butanol; and

b) a slipping layer of Emralon 329® (a dry film lubricant ofpoly(tetrafluoroethylene) particles) (Acheson Colloids Co.) (0.59 g/m²),BYK-320® (a polyoxyalkylene-methyl alkyl siloxane copolymer)(BYK ChemieUSA)(0.006 g/m²), PS-513® (an aminopropyl-dimethyl-terminatedpolydimethylsiloxane) (Petrarch Systems, Inc.) (0.006 g/m²), S-232 (amicronized blend of polyethylene and carnauba wax particles (ShamrockTechnologies, Inc.) (0.016 g/m²) coated from a toluene, n-propylacetate, 2-propanol and 1-butanol solvent mixture. ##STR1##

To evaluate relative printing efficiency using a thermal head, thedye-donors were printed at constant energy to provide a mid-scale testimage on each dye-receiver. By comparison of the dye-densities producedat constant energy, the relative efficiency of transfer is comparable.

The dye side of the dye-donor element approximately 10 cm×15 cm in areawas placed in contact with the polymeric receiving layer side of thedye-receiver element of the same area. The assemblage was fastened tothe top of a motor-driven 56 mm diameter rubber roller and a TDK ThermalHead L-231 (No. 6-2R16-1), thermostated at 26° C., was pressed with aforce of 36 Newtons against the dye-donor element side of the assemblagepushing it against the rubber roller.

The imaging electronics were activated and the assemblage was drawnbetween the printing head and roller at 7 mm/sec. coincidentally, theresistive elements in the thermal print head were pulsed at 128 msecintervals (29 msec/pulse) during the 33 msec/dot printing time. Thevoltage supplied to the print head was approximately 23.5 v with a powerof approximately 1.3 watts/dot and energy of 7.6 mjoules/dot to create a"mid-scale" test image of non-graduated density (in the range 0.5-1.0density units) over an area of approximately 9 cm×12 cm. The Status AGreen reflection density was read and recorded as the average of 3replicates. The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Relative Printing Efficiencies of Receiver                                    Elements with Different Core Layers                                           (see Table 1)                                                                 Sample #  Status A Green Reflection Density                                   ______________________________________                                        1         0.71                                                                2         0.44                                                                3         0.68                                                                4         0.34                                                                ______________________________________                                    

As can be seen from the results in Table 2, the samples described inthis invention can function as thermal dye transfer receivers. Thesesamples were prepared using only coextrusion and lamination processes.The data show that thermal dye transfer receivers can be applied tosupports as thin layers in a process not involving solvent coating.

Example 2

Composite films were prepared by coextruding the following structure:

    ______________________________________                                                            Extrusion Temperature                                     Polymer             (°C.)                                              ______________________________________                                        64 μm Thick COPOL ® Dye Receiver                                                           250                                                       Layer                                                                         Optional 64 μm Thick Admer ® AT                                                            250                                                       507 Tie Layer                                                                 762 μm Thick Poly(Ethylene                                                                     282                                                       Terephthalate)                                                                ______________________________________                                    

These films were coextruded with the temperature profile shown above andcast onto a 9° C. chilled drum and quenched, then stretched 3.3 times inboth the machine and cross directions at 105° C. They were then heat setat 110° C. and rolled up onto a core. The film variations which wereprepared are described in Table 3.

                  TABLE 3                                                         ______________________________________                                        Receiver Elements With and Without Tie Layer                                  on Poly(Ethylene Terephthalate) Core Layers.                                  Receiver material: COPOL ®.                                               Sample #  Tie Layer  Core Layer                                               ______________________________________                                        5         none       Poly(Ethylene Terephthalate)                             6         AT 507     Poly(Ethylene Terephthalate)                             ______________________________________                                    

Each of these films was then hot melt laminated onto a support with a 76μm thick sheet of a linear saturated polyester hot melt adhesive film(Bostik® 10-304-2 from Bostik Corp.). The support was poly(ethyleneterephthalate) (100 μm thick Estar supplied by Eastman Kodak Co.

The printing efficiencies were determined for these samples as inExample 1 except they were printed to full Dmax. The results are shownin Table 4.

                  TABLE 4                                                         ______________________________________                                        Relative Printing Efficiencies of Receiver                                    Elements Without and With a Tie Layer                                         (see Table 3)                                                                 Sample #  Status A Green Transmission Density                                 ______________________________________                                        5         1.54                                                                6         1.31                                                                ______________________________________                                    

As can be seen from the results in Table 4, the samples described inthis invention can function as thermal dye transfer receivers. Thesesamples were prepared using only coextrusion and lamination processes.These data show that thermal dye transfer receivers can be applied tosupports as thin layers without the solvent coating process.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

What is claimed is:
 1. A process for making a thermal dye transferreceiver element consisting essentially of the following steps:a)coextruding a polymeric dye image-receiving layer with an orientablethermoplastic resin to form a cast film; b) stretching said cast film toreduce the thickness of said dye image-receiving layer and to produce anoriented composite film; and c) laminating said oriented composite filmto a support to produce said thermal dye transfer receiver.
 2. Theprocess of claim 1 wherein said orientable thermoplastic resin is apolyolefin.
 3. The process of claim 1 wherein a tie layer is coextrudedwith said dye image-receiving layer and said orientable thermoplasticresin layer.
 4. The process of claim 1 wherein said orientablethermoplastic resin is microvoidable.
 5. The process of claim 1 whereinthe thickness of said composite film is from 30 to 70 μm.
 6. The processof claim 1 wherein said orientable thermoplastic resin layer comprisesfrom 30 to 85% of the thickness of said composite film.
 7. The processof claim 1 wherein the overall density of said composite film is from0.3 to 0.7 g/cm³.
 8. The process of claim 1 wherein said supportcomprises a non-voided polymer film.
 9. The process of claim 1 whereinsaid support comprises cellulose fiber paper.
 10. The process of claim 9wherein said paper support is from 120 to 250 μm thick and saidcomposite film is from 30 to 50 μm thick.
 11. The process of claim 9further comprising a polyolefin backing layer on the side of the supportopposite to said composite film.
 12. The process of claim 11 whereinsaid polyolefin backing layer is present at a coverage of from 35 to 75g/m².
 13. The process of claim 12 wherein the thickness of saidcomposite film is from 30 to 70 μm.
 14. The process of claim 12 whereinsaid support is a cellulose fiber paper support from 120 to 250 μm thickand said composite film is from 30 to 50 μm thick.
 15. The process ofclaim 1 wherein said orientable thermoplastic resin layer of saidcomposite film comprises a microvoided and oriented thermoplasticpolymer and a polymeric void-initiating material.